1. Field of the Invention
The present invention relates to a sector data decoder in a CD-ROM drive. More particularly it relates to a sector data decoding method and circuit in a CD-ROM drive in which two error correction modules using error correction parity information located within sector data are provided for performing error correction in parallel. Using two error correction modules shortens the time required for decoding the sector data, thereby providing the capability to correspond with a high-speed host computer, which follows the current trend of attaining high-speed operation of a CD-ROM. The present application is based upon Korean Application No. 20634/1996, which is incorporated herein by reference.
2. Description of the Related Art
A decoding circuit according to a conventional technique is constructed as shown in FIG. 1. The decoding circuit of FIG. 1 includes an input data storing unit 101 for storing in an external memory 102 data input from a CD-DA unit of a preprocessing portion of a CD-ROM, an error correcting unit 103 for correcting an error in sector data, and a host data transmitting unit 104 for transmitting data to a host computer.
Referring to FIG. 1, generally, the error correction process begins after storing in external memory 102 one sector data of the input sector data. At this time, L-plane and R-plane data corresponding to the same offset are simultaneously read out from external memory 102, error correction is independently executed with respect to the data separated into the L-plane and R-plane, and the result is stored in external memory 102. FIG. 4 represents 1170 bytes of data which correspond to the L-plane, from among 2340 bytes which correspond to 2352 bytes of sector data less 12 bytes of SYNC data. The R-plane data has the same format as the L-plane data and accounts for the other 1170 bytes of non-SYNC sector data.
Here, the L and R-planes (L/R-planes) are processed by the same error correcting process which is carried out in such a manner that a Q code word correction operation is first executed prior to execution of a P code word correction operation. The P code word consists of a total of 43 code words, in which each of the code words consists of 26 bytes. Also, Q code words number 26 in total, and each of those code words consists of 45 bytes.
In the conventional error correcting process discussed above, as shown in FIG. 3, the 26 Q code words of the L-plane are subjected to correction prior to correction of the 43 P code words of the L-plane. Then, correction of the Q and P code words is carried out with respect to the R-plane. That is, correction of the Q and P code words is repeatedly performed with respect to the L/R-planes.
When performing such an error correcting process, all data is read out from external memory 102 and input to error correcting unit 103. Thereafter, the error value is calculated and the result is stored in external memory 102. However, this process involves frequent access of the external memory which has the effect of impeding operations other than error correction in using external memory 102. Besides, the operation of input data storing unit 101, error correcting unit 103 and host data transmitting unit 104 are independently executed with respect to data stored in external memory 102 in units of one sector data.
Generally, a digital data signal processing section of a CD-ROM system is largely divided into a plane decoder and a sector data decoder of the CD-DA unit. Here, data received from the plane decoder is rearranged in the form of sector data to be stored in external memory 102. When one sector data (of 2352 bytes) is completely stored by input data storing unit 101, error correction is performed by error correcting unit 103. At this time, one sector is divided into the L/R-planes, and the error correcting process is carried out twice to store the result in external memory 102 again. Upon finishing the error correcting process, the corrected data is transmitted to the host computer via host data transmitting unit 104, so that the operation of the sector data processing unit of the CD-ROM is completed.
The sector data format used is illustrated in FIG. 3, and the plane format of the sector data subjected to error correction is illustrated in FIG. 4.
However, error correction is performed by dividing one sector data stored in external memory 102 into two left and right L/R-planes, in which, after the error correction process for the first plane is completed, the second plane is subjected to error correction. The time taken for performing the foregoing two steps is being given much weight along with attaining the high speed trend in the CD-ROM system. Due to this fact, the error correcting pattern has significantly hindered heightening the processing speed when being changed into the high-speed system.